X-ray apparatus



July 4, 1939. R MACHLETT 2,164,997

'x-RAY APPARATUS Filed Sept. 8, 1957 kmm 2 ATTORNEY;

Patented July 4, 1939 UNITED STATES PATENT OFFICE X-RAY APPARATUS Raymond B. Maehlett,

Riverside, Conn, assignor Application September 9 Claims.

This invention relates to X-ray apparatus of the kind in which oil is employed as a means for carrying off and dissipating heat generated at the focal spot on the anode during operation.

More particularly, the invention is concerned with an apparatus of the type referred to containing a novel cooling means, the use of which offers numerous advantages both in the construction of the apparatus and in its use. lhe principles of the invention may be employed in X-ray apparatus of various kinds, including those in which the tube is of the self-cooling type and those in which the cooling is effected by circulation of the oil through a passage in the anode. The invention oifers special advantages, however, in connection With shockproof apparatus containing a self-cooling tube, and an embodiment of the invention in that form will, according, be described in detail for purposes of explanation. It is to be understood and will be readily apparent that the utility of the invention is not limited to apparatus of that specific type.

Shockproof X-ray apparatus, as heretofore commonly constructed, includes a grounded metal container for the tube, the container having entrance insulators to insulate the high voltage leads which connect the tube terminals to the supply cables outside the container. The tube is mounted within the container immersed in oil, and the oil serves both as a cooling means and as insulation for the high voltage connections within the container. Apparatus of this type is ordinarily of relatively large dimensions, being both bulkier and heavier than units which are not shockproof, and as a result, its use has been somewhat restricted because, among other things, its relatively great Weight and bulk make it necessary to employ special stands or other supporting devices.

In ordinary X-ray equipment containing a self-cooling tube operating in air, the anode of the tube has a heavy copper shank which eX- tends from the interior of the tube out through the envelope and a copper radiator is mounted on the exposed end of the shank. With air used as the cooling medium, the tube may be safely operated under conditions such that the anode shank and radiator reach relatively high temperatures of the order of 500 0., since the heat dissipation is rapid because of the large temperature difference, even though the air is a relatively inefficient cooling medium. When such a tube is employed immersed in oil in shockproof apparatus of the prior type, the cooling conditions are quite different and it is not permissible 8, 1937, Serial No. 162,839

to operate the tube so that the anode shank and radiator, if one is used, attain temperatures of the values above referred to. The efliciency of the oil as a cooling medium is much better than that of air, and the cooling rate in oil is, therefore, higher than that in air, but the anode temperature imposes limitations on the conditions'of operation. Accordingly, if the ability of the oil to Withstand high temperatures were increased, important advantages would result in that the tube could be operated at a higher energy rating.

Oil is obtainable for use in shockproof apparatus which has an electrical breakdown value of 45,000 volts for a thickness of 0.10", but in the prior practice, clearances of the order of 2" or more through the oil are employed to insulate against voltages of about 45,000. The reason for using such large clearances is that, after the oil has been placed in the container and subjected to the temperatures developed in the operation of the tube, it loses its original good dielectric properties to a substantial extent and a large factor of safety in the clearances is therefore necessary. The requirement that such large clearances be employed can only be met by making the container of heavy, bulky design, and heretofore it has not been possible to construct shockproof equipment which is satisfactory in operation except along the lines pointed out.

I have found that the degeneration of the oil employed in equipment of the type referred to apparently results from chemical changes, such as oxidation, in the oil, which cause the formation of a gummy film on the heated metallic surfaces of the anode shank and radiator, if used, and also render the oil capable of absorbing any moisture that may be present. The formation of the film on the surfaces to be cooled impairs the efficiency of the oil as a cooling agent, and the absorption of moisture reduces its dielectric value to a great extent. While the elimination of the presence of moisture and air from the container are helpful in preventing or at least delaying the degeneration of the oil, there always seems to be a sufiicient amount of oxygen within the oil itself to bring about the undesirable changes, provided the heated metal in contact with the oil is copper. Apparently, copper functions under the conditions described as a catalytic agent Whioh promotes the degeneration of the oil, and it ultimately produces this effect regardless of the steps that have heretofore been taken to keep the oil from being degraded.

The present invention is accordingly directed to the provision of a novel shockproof X-ray apparatus which is smaller, more compact, and lighter in Weight than similar apparatus as heretofore constructed, and in the apparatus of the invention, these objects are attained in part by protecting the oil from the action of parts made of material, such as copper, tending to promote degeneration of the oil. With the parts thus rendered inert with respect to the oil, the electrical clearances required are greatly reduced and, in addition, the apparatus may be operated at higher energy ratings, since the cooling efiiciency of the oil is not impaired during the service.

For a better understanding of the invention, reference may be had to the accompanying drawing, in which the single figure illustrates one form of shockproof unit constructed in accordance with the principles of the invention, the device being illustrated partly in section and partly in elevation.

In the drawing, the apparatus illustrated includes a metal casing i having end openings closed by caps Z secured in place against sealing washers 3 by threaded bushings 4. The casing is provided with the usual necks 5, in which the cable terminals are housed in insulators 6 and held in place by suitable means, and within the main body of the casing is an X-ray tube 1 of the conventional self-cooling type, provided with the usual anode 8 and incandescent cathode 9.

The anode has a heavy shank l sealed through the tube envelope H by a suitable seal l2, and the shank is of sufficient cross-sectional area to be effective to carry away the heat generated at the focal spot. The anode shank is secured rigidly by a metallic strap it to the cable terminal member i l and may bear the entire weight of the tube. At the other end, the tube is provided with the usual lead-in wires sealed through the wall of the envelope and leading to the cable terminal member iii. If desired, the cathode end of the tube may be received within a bushing ll attached to the terminal member iii and serving as a centering means. The tube is disposed within the usual shield l8 having an opening for the emission of rays, the latter passing out of the casing through an opening closed by a window I9. The casing is also provided with an adapter plate 20, by which the casing may be secured to a suitable tube stand. The casing is filled with oil of suitable dielectric quality and as the oil is heated up and expands, it collapses a bellows 2! in a chamber 22 leading from the casing. At abnormal temperatures, the bellows operates against a spring to raise a signal to a position in which it is visible through an opening 23 in a cap 25 at the end of the chamber.

The anode shank ll] of tubes of this type is ordinarily made of copper because of its electrical and heat conductivity, but I have found that the exposed portion of such a copper shank functions at the temperature of operation of the tube as a catalytic agent, which promotes degeneration of the oil. This objectionable feature is overcome in the new tube by providing the exposed portion of the shank with a coating 25 of a material which is inert to the oil, that is, is ineffective at the operating temperature, to promote the degradation of the oil. One coating material which may satisfactorily be employed for the purpose is nickel and I prefer to employ a plating of nickel because of the facility with which it can be applied. Various other metals and materials, however, produce satisfactory results, such, for example, as lead, chromium, stainless steel, and stable metallic oxides, such as alumina. Any material which does not act upon the oil to promote its degeneration is suitable for the purpose and it is not necessary that the coating be of an electroconductive material.

By the use of the coating on that portion of the anode shank, which would otherwise be in contact with the oil, the original dielectric value of the oil is indefinitely preserved. As a consequence, the container may be so constructed that electrical clearances much smaller than those usually adopted can be employed. Thus, for a tube operating at 90,000 volts, it is entirely satisfactory to use clearances of the order of 1" or less instead of 2" or more as has previously been customary. In addition, since the deposition of a gummy film on the exposed portion of the anode shank is prevented, the original cooling efiiciency of the oil is indefinitely maintained, and as a consequence, the tube may be operated at much higher energy ratings than are permissible with corresponding tubes employed in the prior equipment. The increase in loading may be as much as twice that heretofore used and thus, the apparatus of the present invention may be about one-half the size and Weight of prior equipment employed for the same general purpose.

The casing containing the tube, its connections, and the oil is preferably filled with oil and sealed in the factory where special equipment, such as vacuum pumps, is available to permit close control of the quality of the original filling. The'casing, with the tube and oil in place, may then be readily transported and handled as a unit and removal of the tube from the casing in the field for servicing can be avoided.

While I have explained an embodiment of the invention which contains an X-ray tube of the self-cooling type, it is to be understood that the invention may also be incorporated in apparatus in which the oil is circulated through the anode by a pump. In such apparatus as commonly constructed the oil comes into contact with hot copper surfaces and degeneration of the oil results. By the use of the invention, the action of the copper on the oil may be readily prevented by providing the hot surfaces with a coating of one of the specified materials which is ineffective to promote degeneration of the oil at the operating temperature.

In the construction of X-ray tubes, the anodes and their shanks are commonly made of copper because of its high heat and electrical conductivity, but silver might be used for the purpose. I have observed that silver seems to act in a manner similar to copper in promoting degeneration of the oil, and should be provided with an inert coating if the advantages of my invention are to be enjoyed.

I claim:

1. An electron discharge apparatus which comprises an electron discharge device having an envelope, an incandescent cathode and an anode within the envelope, a copper shank leading from the anode through the wall of the envelope, the shank having a heat conductivity sufficient to conduct heat from the anode effectively to the outside of the envelope, a grounded container for the device, a body of oil in the container within which the device is immersed with the portion of the shank outside the envelope giving up heat to the oil, and a coating on all surfaces of the shank which would otherwise be in contact with the oil, the coating being of a material with which the body of oil will remain in contact at the temperature of operation without degeneration and loss of dielectric value.

2. The combination of an electron discharge device having an envelope, an incandescent cathode and an anode within the envelope, a body of oil, said anode including a portion extending to the exterior of the envelope 'and into said body of oil, the entire surfaces of said portion of the anode exterior of said envelope which otherwise would be in contact with said oil being coated with a substance with which the body of oil will remain in contact at the temperature of operation without degeneration and loss of dielectric value.

3. The combination of an electron discharge device having an envelope, an incandescent cathode and an anode within the envelope, a body of oil, said anode including a portion extending to the exterior of the envelope and into said body of oil, the entire surfaces of said portion of the anode exterior of said envelope which otherwise would be in contact with said oil being coated with nickel, whereby the body of oil will not undergo degeneration and loss of dielectric value at the temperature of operation.

4. The combination of an electron discharge device having an envelope, an incandescent cathode and an anode within the envelope, a body of oil, said anode including a portion extending to the exterior of the envelope and into said body of oil, the entire surfaces of said portion of the anode exterior of said envelope which otherwise would be in contact with said oil being coated with chromium, whereby the body of oil Will not undergo degeneration and loss of dielectric value at the temperature of operation.

5. The combination of an electron discharge device having an envelope, an incandescent cathode and an anode within the envelope, a body of oil, said anode including a portion extending to the exterior of the envelope and into said body of oil, the entire surfaces of said portion of the anode exterior of said envelope which otherwise would be in contact with said oil being coated with a stable metallic oxide with which the body of oil will remain in contact at the temperature of operation Without degeneration and loss of dielectric value.

6. The combination of an electron discharge device having an envelope, an incandescent cathode and an anode within the envelope, a body of oil, said anode including a portion of copper extending to the exterior of the envelope and into said body of oil, the entire surfaces of said copper portion of the anode exterior of said envelope which otherwise would be in contact with said oil being coated with a substance with which the body of oil will remain in contact at the temperature of operation without degeneration and loss of dielectric value.

7. The combination of an electron discharge device having an envelope, an incandescent cathode and an anode within the envelope, a body of oil, said anode including a portion of copper extending to the exterior of the envelope and into said body of oil, the entire surfaces of said copper portion of the anode exterior of said envelope which otherwise would be in contact with said oil being coated with nickel, whereby the body of oil will not undergo degeneration and loss of dielectric value at the temperature of operation.

8. The combination of an electron discharge device having an envelope, an incandescent cathode and an anode within the envelope, a casing enclosing the anode end of said envelope, and a body of oil in said casing, said anode including a portion of copper extending to the exterior of the envelope and into said body of oil, the entire surfaces of said copper portion of the anode exterior of the envelope which otherwise would be in contact with said oil being coated with a substance with which the body of oil will remain in contact at the temperature of operation without degeneration and loss of dielectric value.

9. The combination of an electron discharge device having an envelope, an incandescent cathode and an anode within the envelope, a grounded container surrounding said envelope, a body of oil within said container, said envelope being immersed in said body of oil, said anode including a portion of copper sufficient to cool the anode effectively extending to the exterior of the envelope and into said body of oil, said device having high voltage connections insulated from the container by said body of oil, the electrical clearances through the oil between said connections and container not substantially exceeding one inch when the device is operated at about 45,000 volts from the high voltage electrode to ground, the entire surfaces of said portion of the anode which extends into the body of oil which otherwise would be in contact with said oil being coated with a substance with which the body of oil will remain in contact at the temperature of operation without degeneration and loss of dielectric value.

RAYMOND R. MACHLETT. 

